Electronic document scanners, copiers, and facsimile machines transform an optical image of a document into an electric signal suitable for storing, displaying, printing or electronic transmission. There is a need to mark certain documents with an "electronic watermark." An electronic watermark is any auxiliary image that will he added to die electronic copy of the original document. The electronic watermark could be a company name or symbol, or it could be information used to track which scanner, copier, or facsimile machine was used to create the reproduction or it could be the name of the person creating the reproduction.